Implement hit tests/client area.

ui/aura/test/mus/test_window_tree.h

Index: ui/aura/test/mus/test_window_tree.h
diff --git a/ui/aura/test/mus/test_window_tree.h b/ui/aura/test/mus/test_window_tree.h
index 6b0995dcc97538696ffa27e6d3cd9c0d7cc08817..9644870bea088eb2c938e280a07533644815143d 100644
--- a/ui/aura/test/mus/test_window_tree.h
+++ b/ui/aura/test/mus/test_window_tree.h
@@ -80,6 +80,12 @@ class TestWindowTree : public ui::mojom::WindowTree {
   // Data from the most recently added/removed transient window.
   const TransientData& transient_data() const { return transient_data_; }
 
+  const gfx::Insets& last_client_area() const { return last_client_area_; }
+
+  const base::Optional<gfx::Rect>& last_hit_test_mask() const {
+    return last_hit_test_mask_;
+  }
+
  private:
   struct Change {
     WindowTreeChangeType type;
@@ -188,6 +194,10 @@ class TestWindowTree : public ui::mojom::WindowTree {
 
   TransientData transient_data_;
 
+  gfx::Insets last_client_area_;
+
+  base::Optional<gfx::Rect> last_hit_test_mask_;
+
   DISALLOW_COPY_AND_ASSIGN(TestWindowTree);
 };